Some fun with the hypothetical ES7 decorators notation (`@xxx`)

es7-decorators

class Class {
  @Bound
  method() {}

  @Lazy
  get data() {}
}

function Bound(prototype, name, descriptor) {
  const { value, writable, enumerable, configurable } = descriptor;

  if (typeof value !== 'function') {
    throw new Error();
  }
  
  const decoratedDescriptor = {
    get() { return value.bind(this) }
    enumerable, configurable
  };
  
  if (writable) decoratedDescriptor.set = function (newValue) {
    overrideWith(this, name, newValue)
  };

  return Lazy(prototype, name, decoratedDescriptor);
}

function Lazy(prototype, name, descriptor) {
  const { get, set, enumerable, configurable } = descriptor;

  if (typeof get !== 'function') {
    throw new Error();
  }

  const decoratedDescriptor = {
    get() {
      const value = get.call(this);
      overrideWith(this, name, value);
      return value;
    },
    enumerable,
    configurable
  };
  
  if (set) decoratedDescriptor.set = set;
  
  return decoratedDescriptor;
}

function overrideWith(target, name, value) {
  const { set, writable, enumerable, configurable } = Object.getOwnPropertyDescriptor(this, name);
  const descriptor = { value, writable: writable || Boolean(set), enumerable, configurable };
  Object.defineProperty(this, name, descriptor);
}